Question

Which of the following properties of Zr and Hf can be explained due to lanthanide contraction?
A.Radius of Zr and Hf is same
B.Their EN is same
C.Their position in periodic table
D.All

Answer 1

Basically, lanthanides are rare earth elements of the modern periodic table. The elements with atomic number 58-71 following the element lanthanum are called rare earth metals. To solve this question, we need to know the properties of the lanthanide elements.

Complete step by step answer:
Lanthanides are highly dense elements, with densities ranging from roughly 6.1-9.8 grams per cubic centimeter. These elements have very high melting and boiling points. Further, the 4f series in the periodic table are known as lanthanides and they are present at the bottom of the periodic table. Some of the properties of these elements are:
1.They are soft metals and can even be cut with a knife
2.They have luster and are silvery in appearance
3.They all mostly form trivalent compounds.
4.They are magnetic in nature
Now, let’s discuss lanthanide contraction. The atomic size or ionic radii of tri positives lanthanide ions decrease steadily from La to Lu due to increase in nuclear charge and electrons entering inner $(n - 2)f$ orbital. So, this gradual decrease in size with an increasing atomic number is known as lanthanide contraction. Now, some of the consequences of lanthanide contraction are:
1.Atomic size- Basically the size of the atom of the third transition series is nearly the same as that of the atom of the second transition series. For example, the radius of Zr= radius of Hf and the radius of Nb=radius of Ta etc.
2.Electronegativity- Generally, the electronegativity increases from La to Lu.
3.Complex formation-The tendency to form complexes, increases from $L{a^{ + 3}}$ to $L{u^{ + 3}}$. This is because of the small size and higher nuclear charge.
Therefore, it is clear that the radius of Zr and Hf is the same.

Hence, option A is correct.

Note: All the elements in the lanthanide series show an oxidation state of +3. But earlier it was believed that some of the metals also show +2 oxidation state. Further studies revealed that all the metals in lanthanide series exhibit +2 oxidation state in their complexes in solutions.